1. Field of the Invention
The present invention relates to a spray painting apparatus for spray-painting an object such as an automobile body, and more particularly to a spray painting apparatus of the above type having a spray nozzle arm pivotably supported to a support unit via a pivot shaft for allowing position adjustment of a spray nozzle by pivoting the arm in accordance with the shape of the object or other operational conditions.
2. Description of the Related Art
A spray painting apparatus of the above-described type is known from e.g. a Japanese patent application No. 63-157717 which is shown in FIG. 5.
In this conventional apparatus of FIG. 5, numeral 10 denotes an arm attached with a spray nozzle 11. Numeral 22 denotes a pivot shaft for operatively connecting the arm 10 to a lift unit 9 which is a support unit for the arm 11. The arm 10 is pivoted about an axis P through rotational drive force of the pivot shaft 22. Further, the arm 10 is reciprocable along the axis P through reciprocating sliding motions of the pivot shaft 22.
The lift unit 9 is liftable with respect to a base mount 8, while the mount 8 is movable along a direction of conveying the object. In summary, this conventional apparatus effects a spray painting operation on the object A while appropriately adjusting the position of the spray nozzle 11 by the combinational movements of: the motion of the base mount 8 along the object-conveying direction, the lifting motion of the lift unit 9, the pivotal motion of the arm 11 about the axis P and the reciprocating motion of the arm 10 along the axis P.
Numeral 35 denotes a valve unit for switching over feed of paint to the nozzle 11. This valve unit 35 is mounted on the lift unit 9 and is connected with a plurality of tubes 36 extending from the base mount 8 to the lift unit 9 so as to selectively feed a plurality of kinds of paint to the nozzle 11 through the valve unit 35.
In all the conventional apparatuses of this type including the one illustrated in and described above with reference to FIG. 5 (another such conventional apparatus is known from a Japanese laid-open patent gazette Serial No. 62-234565), the pivoting operation of the arm 10 is effected through the rotational drive of the pivot shaft 22 which supports the arm 10 to the support unit. In such apparatuses, there occurs disadvantageous concentration of the load of the arm 10 on the pivot shaft 22 and there arises also concentration of the reaction moment of the arm 10 (resulting from the pivotal motion of the arm 10) on this pivot shaft 22. As a result, there tends to occur excessive deformation in this pivot shaft 22 (i.e. elastic deformation and plastic deformation in the shaft periphery). This exessive deformation in the shaft 22 eventually makes it difficult or even impossible to accurately position the nozzle 11 with respect to the object to be painted; and such inaccurate positioning of the nozzle 11 necessarily leads to deterioration in the painting quality of the object.
Then, the primary object of the present invention is to overcome the above-described drawback of the convention through rational improvement of the pivot mechanism for the nozzle arm.